1. Field of the Invention
The present invention relates to a tape cartridge for digital recording with a DDS (Digital Data Storage), a DAT (Digital Audio Tape) or another medium used.
2. Discussion of Background
In such a type of conventional tape cartridge, a pair of hubs with a tape-shaped medium wound thereon are rotatably supported in a casing. In FIGS. 8(a), 8(b), and 8(c), a bottom plan view, a cross-sectional view taken along line 8b--8b of FIG. 8(a), and a top plan view, respectively, show an example of conventional hubs. Each hub 103 comprises a dram 103a at an outermost side and an inner cylinder 103b formed inside of and integrally with the drum 103a The drum 103a is a portion that has a tape-shaped medium wound on an outer periphery thereof.
The inner cylinder 103b has a bore 103e formed therein to accept a driving shaft of a recording/reproducing device. The hub 103 has teeth 103d formed on an outer periphery of an upper portion thereof to be engageable with a pawl of a hub brake. When the pawl of the hub brake have leading edges engaged into between teeth 103d, the hub 103 is locked against rotation.
In FIGS. 9(a) and 9(b), a plan view and a cross-sectional view taken along line 9b--9b of FIG. 9(a), respectively, show a state wherein the driving shaft of a recording/reproducing device is inserted into the bore 103e of the inner cylinder 103b of the hub 103. The inner cylinder 103b has six projections 103c provided on an inner peripheral surface thereof in a peripheral direction at equal intervals to extend in a vertical direction. The driving shaft 110 has a core or root 111 and three engaging portions 112. The engaging portions 112 are provided on an outer peripheral surface of the driving shaft 110 at equal intervals to extend in the vertical direction. When the driving shaft 110 is inserted into the bore 103c of the hub 103, the respective engaging portions 112 are located between projection 103c to transmit rotation from the driving shaft 110 from the engaging portions 112 to the projections 103c, rotating the hub 103./
Recently, there have been demands to provide a tape cartridge having larger storage capacity for data storage. In order to increase the storage capacity, a tape-shaped medium is required to have a thinner thickness than conventional ones, allowing a greater tape length to be accepted. However, such a tape-shaped medium has a thickness limitation of about 5 .mu.m in terms of production technique. From this viewpoint, the outer diameter of the drum 103a is required to be smaller than the conventional ones, allowing the tape length to be extended under the limitation.
The drum 103a is subjected to slow thermal shrinkage since the drum is thicker than surrounding parts. As a result, a phenomenon that a recess is formed by thermal shrinkage occurs in the drum in many cases. In order to prevent this phenomenon from occurring, preformed recesses 103f are formed in the drum. In order to prevent the occurrence of a recess due to thermal shrinkage in the drum 103a at the time of molding the drum, the preformed recesses 103f are formed in upper and lower portions of the drum to ensure that the drum 103a has a proper wall thickness. If the outer diameter of the drum 103a is decreased, the preformed recesses 103f are made smaller, creating problems in that the strength of portions of a mold for forming the preformed recesses 103f is weakened and that the form accuracy of the drum 103a is lowered.
It is an object of the present invention to make the outer diameter of drums smaller to wind a longer tape-shaped medium thereon without lowering the strength of a mold and the form accuracy of the drums.
In order to solve the problem, the present invention provides a tape cartridge comprising a pair of hubs, the respective hubs including respective drums for winding a tape-shaped medium thereon and respective inner cylinders with respective driving shaft insertion bores for accepting respective driving shafts of a recording/reproducing device, the respective inner cylinders being integrally molded with the respective drums; a casing including upper and lower halves, the casing rotatably supporting the hubs therein; driving shaft insertion holes formed in the casing, the respective driving shaft insertion holes accepting the respective driving shafts; a slider for slidably covering the respective driving shaft insertion holes; a hub brake engageable with the hubs; teeth provided on upper portions of the respective hubs so as to be engageable with the hub brake; recesses formed between the respective drums and the respective inner cylinders, the recesses having upper ends thereof opened; the respective drums having respective outer peripheral surfaces between adjoining teeth conformed to inner peripheral surfaces of the respective recesses; and the respective teeth having portions thereof extending into the respective recesses.